Watch What You Eat, Using Your Phone as a Guide

I have always been skinny, but I do need to watch what I eat. So I count my calories — with the help of smartphone and tablet apps.

One of the best is Calorie Counter & Diet Tracker by MyFitnessPal. Free on iOS and Android, it’s full of features for tracking food intake and exercise.

The app asks basic questions about height, weight, age, exercise levels and target weight, and uses this data to calculate a sensible daily calorie intake. You are supposed to enter the calorie values of everything you eat; the app then helps you avoid overshooting your daily allowance.

The app has a bar code scanner so it can look up most nutritional information directly from food packaging. This worked surprisingly well for me, getting the right information for everything from Heinz tomato soup to a Portuguese variant of the French cheese La Vache Qui Rit. All you have to do is enter how much you have eaten of a particular food to help the calorie calculation.

The scanner does not work all the time, so there is also a manual interface to enter the data. For each new food item, you type in the brand name, calorie count, fat content, salt content and so on. It’s slow, but you enter the data only once.

If you are really in a rush, or are estimating the calories in a restaurant meal, you can skip all this and just add the total calories.

Calorie Counter also tracks your exercise regime and includes this with your daily calorie count. If you need nutritional advice, the app can tell you the healthfulness of the food you are eating, based on the nutritional data it has gathered.

Its interface is simple, though not especially elegant, and it can feel a bit clinical. And Calorie Counter works best when you put in a lot of effort.

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Left to right, Calorie Counter PRO from MyNetDiary tracks a user’s eating habits and exercise; Eatly evaluates food based on a photo and users’ ratings; MyFitnessPal’s Calorie Counter app can suggest a sensible daily intake.

A similar but simpler app with a friendlier interface is Calorie Counter PRO by MyNetDiary, $4 on Android and iOS. It calculates your suggested calorie intake and helps you track eating habits and exercise sessions. A search function can look up common brands and grab their nutritional data from the web. It also has a bar code scanner feature but, as with the MyFitnessPal app, its reliability can vary.

In general Calorie Counter PRO feels like its better-known rival, but you may find you can work with it more quickly. Also, it looks nicer.

A similar offering on Android is Calorie Counter by FatSecret. This app is also attractively designed and features the same tricks of logging food and exercise. It’s free.

While all the diet apps are very hands-on, some add more automation. One is Meal Snap, a $3 iOS app, and when it works it can seem magical.

The app creates a daily food diary for you by recognizing the food from photos you shoot. It is supposed to be as simple as that. You take a picture, dial in data such as whether you are eating breakfast or lunch and add a quick text label, and the app estimates the calorie content.

Many reviewers say it does a pretty good job, although its estimate can be a bit unpredictable. It also needs a network connection, which is something to think about when eating out.

Eatly takes less effort. It also uses photos of food, but instead of estimating actual calorie counts it simply rates the food from “very healthy” through “it’s O.K.” to “unhealthy.” The app’s community of users does the rating, and you can take part by rating other users’ photos.

Eatly is supposed to teach you to recognize healthy foods. Call it crowdsourced peer pressure. The app is well designed and fun to use, but it may not offer everything you need to balance food and exercise. It’s free on iOS and Android.

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A version of this article appears in print on , on Page B7 of the New York edition with the headline: Watch What You Eat, Using Your Phone as a Guide. Order Reprints | Today’s Paper | Subscribe